Heretofore, as substrates for a displays such as liquid crystal display elements or organic ELs, it has been attempted to employ a various types of film substrates for the reasons that their shapes can be easily changed, they enable displays in a curved plane and these substrates are light in weight (refer to e.g. Patent Document 1 or 3).
However, such a film substrate has a problem that it was inferior to a glass in gas barrier property. In order to use a film substrate as a substrate for a display such as a liquid crystal display device or an organic EL, it is necessary for the film substrate to have high gas barrier property to prevent deterioration of the device. Particularly in order to use a film substrate for organic EL, the film substrate is required to have a water vapor permeability of at most 5×10−5 g/m2/day that is a strict requirement not comparable to those for packing members. Conventional gas permeability measurement apparatuses can perform quantitative evaluation of only as low as 5×10−3 g/m2/day. To cope with this problem, a new gas permeability measurement method using property change of metal Ca is proposed in Non-Patent Document 4.
As a substrate having gas barrier property, a film substrate provided with a specific resin (refer to e.g. Patent Document 1), and a film substrate provided with a resin layer composed of a fluorine compound (refer to e.g. Patent Document 3) are disclosed. However, these substrates do not have sufficient gas barrier properties.
Further, a multilayer gas barrier film constituted by alternately laminated inorganic compound films and resin films 1 inserted between the organic compound films, is proposed (refer to e.g. Patent Document 5). However, since defects such as pinholes formed in a first layer affect the next layer, it is difficult to reduce defect density that significantly affects gas barrier property. Further, there is also a problem that sideward gas barrier property at edges of the film is not sufficient.
Besides this multilayer film, a film substrate provided with a multilayer film made of an inorganic compound such as silicon nitride oxide or silicon nitride, is disclosed (refer to e.g. Patent Document 6). However, since it is necessary to form the multilayer film made of several types of inorganic compound by several types of film-forming methods, there is a problem that the film forming speed is low and the productivity is low.
Further, in recent years a new display device has been being looked forward, which replaces conventional display devices such as CRTs. Among these, especially, an organic EL display has a merit that it realizes high intensity emission even at an applied voltage of less than 10 V, it enables light emission with a simple element structure, and it realizes a display of smaller thickness even compared with a liquid crystal display element. Accordingly, such an organic EL display is expected to be used for such applications as a display for advertisement which emits light of a predetermined pattern, a simple display of low cost or a full color display.
An organic EL element has a construction that an anode, a hole injection layer, a hole transportation layer, a light emission layer and a cathode are laminated in this order, and is usually formed on a transparent substrate. In such an organic EL element, materials of the organic light emission layer or the cathode are deteriorated by moisture or oxygen in the atmospheric air, and accordingly, deterioration of light intensity or generation of defects such as dark spots are pointed as problems. Accordingly in order to prevent deterioration of such an element, it is necessary to seal the element with high gas barrier performance. Especially in order to use a member as a sealing substrate for an organic EL display, the member is required to have a water vapor permeability of 5×10−5 g/m2/day in terms of permeability to the inside of the sealing substrate, that is a strict requirement not comparable to those of packing members.
In an organic EL display of bottom emission type having a light output plane on a transparent substrate side, as a method for preventing deterioration of performance due to moisture or oxygen, a method of sealing a drying agent in the device by a sealing cap made of a metal or a glass, is disclosed (refer to e.g. Patent Document 7). Further, it is disclosed that such a drying agent is preferably an inert liquid constituted by a fluorocarbon oil mixed with a dehydrating agent such as a synthetic zeolite (refer to e.g. Patent Document 8). However, in each of these methods, sealing step is complicated and productivity is poor. Further, there is a problem that since a sealing substrate itself is thick, the thickness of display is increased. For these reasons, in order to overcome these problems, besides a method of absorbing moisture entered into an element, a sealing capable of preventing intrusion of moisture is looked forward.
As an invention of such a sealing, a sealing achieved by a special resin provided on a transparent substrate (refer to e.g. Patent Document 1) and a sealing achieved by a resin composed of a fluorine compound provided on a transparent substrate (refer to e.g. Patent Document 3) are disclosed. However, these sealings do not provide sufficient gas barrier property.
Further, as another invention, a sealing achieved by a special inorganic compound film formed on a substrate, specifically, by a film composed of alumina or silicon nitride, is proposed. However, since each of these films usually has a small film thickness of tens of nms, and it is difficult to form a dense film, there is a problem that it is difficult to avoid generation of pinholes by a single layer.
In order to compensate this demerit, a multilayer film is proposed, which has a construction that inorganic compound films and resin films inserted between the inorganic compound films are alternately laminated (refer to e.g. Patent Document 5). However, an inorganic compound film has a problem that defects such as pinholes tend to be formed in such a film, and e.g. these pinholes significantly affect gas barrier property of the next layer, and accordingly, it is difficult to reduce defect density. Further, there is also problem that its productivity is poor.
Besides the above films, a multilayer film constituted by a lamination of inorganic compound films of e.g. silicon nitride oxide or silicon nitride, is disclosed (refer to e.g. Patent Document 6). However, this multilayer film does not have sufficient gas barrier performance. Further, since the process for forming such a multilayer film is complicated and its productivity is low, its cost tends to be high. Further, there is also a problem that film-forming speeds of these inorganic compound films are low and their productivities are poor. Further, it is necessary to sequentially laminate several layers to form a multilayer film. In a case of forming a multilayer film on an organic EL element, layers are formed on an upper surface of the element and there will be no problem on the upper surface, but it is difficult to regularly form layers on side portions of such an organic EL element, and there is a problem that gas barrier property on side portions is insufficient.
Patent Document 1: JP-A-2003-335820
Patent Document 2: WO03/094256
Patent Document 3: JP-A-2003-340955
Patent Document 4: JP-A-2003-340971
Patent Document 5: WO00/36665
Patent Document 6: JP-A-2004-119138
Patent Document 7: JP-A-5-182759
Patent Document 8: JP-A-5-41281
Non-Patent Document 1: M. Benmalek, H. M. Dunlop, “Inorganic coatings on polymers”, Surface and Coatings Technology 76-77, (1995), pp 821-826.
Non-Patent Document 2: Yoji Kawamoto, Shoji Tsuchihashi, “Glass-Forming Regions and Structure of Glasses in the System Ge-S” J. of The American Ceramic Society vol. 52, No. 11, (1969), pp 626-627.
Non-Patent Document 3: Andreas Weber, Silke Deutschbein, Armin Plichta, “Thin Glass-Polymer Systems as Flexible Substrates for Displays”, SID 02 Digest, (2002), pp 53-55.
Non-Patent Document 4: G. Nisato, P. C. P Bouten, P. J. Slikkerveer, W. D. Bennet, G. L. Graff, N. Rutherford, L. Wiese, “Evaluating High Performance Diffusision Barriers: the Calcium Test”, Asia Display/IDW '01 Proceedings, (2001), pp 1435-1438.